Realistic Gastly

Gastly is born in a leathery eggshell, layed in areas where death is abundant (cemetaries and such). As the egg matures, its outer shell becomes porous, and the gases given off by the decaying bodies surrounding its nest accumulate around the egg. The egg does not hatch; instead it becomes the main body--its only outer features are its large eyes and larger gaping maw. The pores in its skin/shell are used to absorb and eject the gases around it, giving it its characteristic hazy appearance and movement capability.

Quick doodle. Hooray for Gastly!

_{It looked way cooler inverted, so, I left it that way.}